Effective cleaning and shaping of the root canal system is essential for achieving the biological and mechanical objectives of root canal treatment (Sjögren et al. 1997). The objectives are to remove all the pulp tissue, bacteria and their by-products while providing adequate canal shape to fill the canal.
Traditionally, the shaping of root canals was achieved by the use of stainless steel hand files. However, techniques using stainless steel hand files have several drawbacks:    1. They require the use of numerous hand files and drills to adequately prepare the canals (Schilder 1974).    2. Hand instrumentation with stainless steel files is time consuming (Ferrazetal. 2001).    3. The stainless steel hand instrumentation techniques have an increased incidence of canal transportation (Kuhn et al. 1997, Reddy & Hicks 1998, Ferraz et al. 2001, Pettiette et al. 2001).    4. Finally, from a clinical standpoint, the use of hand instruments in narrow canals can be very frustrating especially in teeth with difficult access.
Moreover, canal curvature has always introduced complexity into canal preparation. The “balanced force concept,” i.e. small clockwise and counter clockwise movements, was developed over a period of 12 years, and proposed in 1985 by Roane as a means of overcoming the curvature influence. Using the balanced force technique, it is possible to shape curved canals with larger diameter hand instruments. The use of stainless steel hand instruments, however, is time-consuming and strenuous, and there is a high frequency of preparation errors.
The development of continuous rotary preparation with nickel-titanium instruments solved some of these issues, although it is still necessary to use several hand and rotary files in different steps, and there may be a lengthy learning curve before proficiency can be achieved. In fact, NiTi instruments offer many advantages over conventional stainless steel files. They are flexible (Walia et al. 1988), have increased cutting efficiency (Kazemi et al. 1996) and have improved time efficiency (Ferraz et al. 2001). Furthermore, NiTi instruments maintain the original canal shape during preparation and have a reduced tendency to transport the apical foramen (Kuhn et al. 1997, Reddy & Hicks 1998, Ferraz et al. 2001, Pettiette et al. 2001).
However, as these techniques also require the use of numerous instruments to enlarge the canal to an adequate size and taper, they are relatively time consuming.
Also, the use of hand instruments (for example to create a glide path prior to using a rotary instrument), which can be very frustrating in narrow canals in teeth with a limited access, is required. With continuous rotary NiTi systems it is necessary to create a glide path in order to minimize the risk of fracture. During the use of a rotary instrument, the tip of the instrument may bind in the canal. The motor will keep rotating the instrument while the tip of the instrument is bound. The instrument will rotate past its plastic limit and will eventually fracture at a specific angle of rotation. For this reason, it is necessary to create an initial glide path, or a minimal canal enlargement, before using continuous rotary instruments. The glide path will minimize the incidence of instrument binding and, therefore, minimize the risk of fracture.
The use of only one engine-driven instrument in reciprocation to prepare a root canal was published in the International Endodontic Journal (Yared 2008). The article described the use of an F2 ProTaper instrument. However, the use of that instrument in reciprocation presented two drawbacks:
1. Instrument fracture by cyclic fatigue in relation to the relative rigidity of the instrument due to its size, taper and cross-section.
2. The necessity of creating a glide path with additional hand files prior to using the F2 instrument in reciprocation.